It started small, half a century ago, but with a mission.

The first New Orleans Jazz & Heritage Festival was held in 1970 in Beauregard Square, previously and afterward known as Congo Square, where African drumming and dancing had persisted through the era of slavery. It was modeled on the traditional-music showcases at the Newport Folk Festival, but filled entirely with Louisiana’s own styles — jazz, blues, gospel, brass bands, zydeco, Mardi Gras Indians and much more. Duke Ellington, the only performer without Louisiana roots, was commissioned to write and perform a “New Orleans Suite.” Nearly two dozen food vendors offered jambalaya, étouffée and other specialties.

Tickets were $3. But only about 300 people showed up, and the overstocked vendors ended up feeding children from a nearby orphanage.

Yet the New Orleans Jazz & Heritage Festival has proved ambitious and resilient: It has survived deficits, rainouts and the aftermath of hurricanes. As it enters its 50th official run on Thursday, Jazz Fest, as everyone calls it, has grown inseparable from the cultural ecosystem of its hometown, embracing the sounds of the city and welcoming outsiders to enjoy them.

“Jazz Fest is everything that you love about New Orleans to begin with,” said Ivan Neville, the keyboardist who made his first appearance there in 1977; he is performing this year with his band Dumpstaphunk and in the Foundation of Funk with the rhythm section of the Meters, the band co-founded in 1965 by his father, Art Neville. “It’s the most variety of music that you’ll ever see in one given place, so that’s first, and then the best food that you will ever eat in your entire life.”

In recent years, Jazz Fest has drawn between 400,000 and 500,000 attendees across its two extended weekends; its peak, in 2001, was 618,000. Festival organizers estimate that it brings $300 million into the New Orleans economy. This year’s event includes nationally known headliners and hitmakers, among them Katy Perry, J Balvin, Chris Stapleton, Diana Ross and Pitbull, as well as habitual Jazz Fest performers including Santana, Bonnie Raitt, Jimmy Buffett, Al Green, Herbie Hancock and the Dave Matthews Band.

Yet while visiting attractions have boosted attendance, they have never defined the festival. Quint Davis, who has booked music for Jazz Fest since it began and is now the C.E.O. of Festival Productions-New Orleans, noted that this year’s lineup includes 688 groups, “and 600 of them are from New Orleans and South Louisiana.”

That dedicated focus on the local is the core of the festival, which has bolstered the sublime stubbornness of New Orleans culture — where continuity is cherished and singular local customs are continued across generations — and brought worldwide appreciation to what were once just neighborhood festivities. “There’s no question that Jazz Fest has been the event that put New Orleans music on the map,” said Jan Ramsey, the publisher and editor in chief of the New Orleans music magazine OffBeat.

Jazz Fest has maintained its mandate because it operates far differently from other American festivals its size. Its music encompasses vintage jazz to chart-topping reggaeton; its audience is genuinely all-ages. It takes place in daylight, ending at 7 p.m. — which not only encourages visitors to seek out night life, but also rules out stage spectacles dependent on lights and video, emphasizing old-school musicianship instead.

More significantly, Jazz Fest is nonprofit, channeling revenues back into Louisiana music. “The mission of the festival all along has been to make a full circle,” Davis said. “To go back and support the culture that you’re promoting.”

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